Oil Seals or Rotary Shaft Seals are designed to provide a barrier to retain lubricant and to keep out contamination. They are available in metric and imperial sizes with a variety of sealing lip arrangements the most common of which are:

R21 - Single Sprung Lip

R23 - Single Sprung Lip with the addition of a wiper lip to help keep out contamination

Oil Seals are constructed using a steel case which is usually covered in rubber. Various materials are available the most common materials are: